The art contains many disclosures on the use of polymer additives in lubricating oil compositions. Ethylene propylene copolymers and ethylene-alpha olefin nonconjugated diene terpolymers which have been further derivatized to provide bifunctional properties in lubricating oil compositions illustrate this type of oil additive.
U.S. Pat. No. 4,089,794 discloses ethylene copolymers derived from ethylene and one or more C3 to C28 alphaolefin solution grafted with an ethylenically-unsaturated carboxylic acid material followed by a reaction with a polyfunctional material reactive with carboxyl groups, such as a polyamine, a polyol, or a hydroxyamine which reaction product is useful as a sludge and varnish control additive in lubricating oils.
U.S. Pat. No. 4,137,185 discloses a stabilized imide graft of an ethylene copolymer additive for lubricants.
U.S. Pat. No. 4,146,489 discloses a graft copolymer where the backbone polymer is an oil-soluble ethylene propylene copolymer or an ethylene-propylene-diene modified terpolymer with a graph monomer of C-vinyl-pyridine or N-vinylpyrrolidone to provide a dispersant VI improver for lubricating oils.
U.S. Pat. No. 4,320,019 discloses a multipurpose lubricating additive prepared by the reaction of an interpolymer of ethylene and a C3-C8 alpha-monoolefin with an olefinic carboxylic acid acylating agent to form an acylating reaction intermediate which is then reacted with an amine.
U.S. Pat. No. 4,340,689 discloses a process for grafting a functional organic group onto an ethylene copolymer or an ethylene-propylene-diene terpolymer.
U.S. Pat. No. 4,357,250 discloses a reaction product of a copolymer and an olefin carboxylic acid via the “ene” reaction followed by a reaction with a monoaminepolyamine mixture.
U.S. Pat. No. 4,382,007 discloses a dispersant-VI improver prepared by reacting a polyamine-derived dispersant with an oxidized ethylene-propylene polymer or an ethylene-propylene diene terpolymer.
U.S. Pat. No. 4,144,181 discloses polymer additives for fuels and lubricants comprising a grafted ethylene copolymer reacted with a polyamine, polyol or hydroxyamine and finally reacted with an alkaryl sulfonic acid.
U.S. Pat. No. 5,932,525 teaches multi-grade lubricating oils comprising a low saturate base stock, less than three mass percent of an ash less dispersant and a viscosity modifier.
U.S. Pat. No. 5,427,702 discloses mixed ethylene alpha olefin copolymer multifunctional viscosity modifiers.
U.S. Pat. No. 4,863,623 teaches multifunctional olefin copolymer VI improvers.
U.S. Pat. No. 5,075,383 discloses a process for preparing a dispersant and antioxidant olefin copolymer additives, wherein free radical grafting is accompanied by the molecular weight reduction of the copolymers due to mechanically shearing.
U.S. Pat. No. 5,556,923 discloses oil solutions of adducted derivatized EPR or EPDM.
In one conventional process, a grafted olefin copolymer VI improver is synthesized by grafting maleic anhydride or other dicarboxylic anhydride on an olefin copolymer in the presence of an alkane solvent, e.g., hexane, or similar hydrocarbon solvent. However, certain solvents, such as alkanes (e.g., hexane) in particular, can undesirably participate in side reactions during the grafting reaction to form undesired side products, such as grafted alkyl succinic anhydrides, which represent impurities in the end product. Also, relatively higher amounts of transient unfunctionalized polymer (ungrafted polymer) can be present after grafting in solvent-based grafting reactions, which reduces the useful activity level of the product.
Emission requirements for all vehicles have become increasingly more stringent. For instance, diesel engine design changes required to meet emission requirements have led to increased levels of soot in engine lubricants. This increased level of soot causes increased wear when oils are not properly formulated. In particular, with the arrival of new exhaust gas recirculation or recycle (hereinafter “EGR”) cooled engines including cooled EGR engines, a problem has developed in the ability of the conventional lubricating oils to handle the resulting increased soot loading. These new engines also have more stringent NOx emission standards. It has been noted in field testing of certain Mack and Detroit Diesel trucks that the engine oils tested in the cooled EGR prototype engines exhibit undesirably excessive oil thickening because of the way soot is being generated. Increasing the treat rate of the standard dispersants in the lubricating oils has not solved the problem. It has been suggested that oils having the capability to form films that are thicker than the size of primary soot particles may be able to prevent or reduce this source of abrasive wear.
U.S. Pat. No. 6,715,473 describes the use of certain olefin copolymers containing alkyl or aryl amine, or amide groups, nitrogen-containing heterocyclic groups or ester linkages in lubricating oil compositions used in EGR equipped heavy duty diesel engines.
Advanced olefin polymer dispersant viscosity index improvers are needed and desired for use in lubricating oils which provide improvements in film formation properties, and deposit and soot control, in lubricants used in internal combustion engines, such as diesel engines and EGR engines in particular.